The present invention relates to a method of controlling a machine in which a motion of a specific portion in one cycle is defined, such as a rotary cutter for continuously cutting web paper, an iron sheet, or the like that successively travels, into a preset length and without stopping the travel, or a continuous packaging machine for performing a sealing work in synchronization with a film, paper, or the like that successively travels, by using a servo motor and producing an electronic cam curve including a prediction to the next cycle.
As a cutting control method for a rotary cutter of the conventional art, for example, known is a motion controller which is disclosed in JP-A-5-337729. FIG. 20 is a control block diagram of the motion controller of the conventional art. The speed and travel distance of a travelling workpiece 215 are converted at an arbitrary ratio by an electronic gear 203, and a pulse distributor (1) 204 produces a command pulse. The cut length of the workpiece is input through a setting device 205, a position correction amount of a rotary blade is obtained by a command data calculating section 206, a correction pulse is output from a pulse distributor (2) 208, and the pulses are combined with each other by a combining circuit 209, thereby performing a servo control.
Specifically, in the case where, as shown in a speed pattern diagram of FIG. 21, the travelling speed of the workpiece 215 is set to V1 as shown in FIG. 21A and the peripheral speed of the rotary blade 213 is adjusted by the S distributor (1) so as to be equal to the workpiece traveling speed V1 as shown in FIG. 21B, the speed is corrected by a speed waveform V2 due to a position correction command for the rotary blade (by an output of the distributor 2) as shown in FIG. 21C because the cut length of the workpiece 215 does not coincide with the peripheral length of the rotary blade, and, as shown in FIG. 21D, a cutting zone is controlled to the same speed as the line speed of the workpiece 215 and a noncutting zone (correcting zone) is additionally controlled to a speed V3=V2+V1.
Furthermore, FIGS. 21E and 21F show a correcting direction in the case of, for example, a long cutting operation in which the cut length is larger than the peripheral length of the blade, and a subtractive control is performed in the deceleration direction. In addition to the rotary cutter, also a lateral sealing mechanism of a vertical continuous packaging machine, or the like can be control driven.
FIG. 22 is a view showing an example of an electronic cam control of the conventional art, and is a control block diagram of an electronic cam which is disclosed in JP-A-7-311609. In the configuration of FIG. 22, a cam curve 319 which is previously prepared in accordance with operation characteristics of a load 313 is input into a CPU 301 of calculating means, and the CPU 301 outputs a position command value (S), a speed command value (V), and an acceleration command value (A) to comparators in which a subtractor is combined with a counter, a V/F converter, or a differentiator, respectively, and performs an F.B. control on the basis of an output pulse of a PG 314 which detects a displacement of the load 313.
In the conventional art examples, in the case of JP-A-5-337729, however, the correction method in which the cut timing is adjusted by adding (in a short cutting operation) or subtracting (in a long cutting operation) a trapezoidal speed corresponding to the difference between the peripheral length and the cut length, to or from the peripheral speed of the rotary blade that is equal to the line speed V1 of the working line is not novel. In contents of the control also, with respect to the position control, an optimum position pattern is not produced by an electronic cam curve or the like. Therefore, the speed control is performed mainly on the basis of the addition or the subtraction of the corrected speed.
In such a trapezoidal speed control, as shown in FIG. 24, particularly in a control of a rotary cutter, the line speed must be reduced in a short cutting operation because the peak of a torque required during acceleration or deceleration is high. This produces a problem in that the productivity is lowered.
In the case of the proposal of JP-A-7-311609, the technique of reducing the follow-up delay as far as possible by means of a control on the basis of the cam curve 319 (position pattern) which is previously prepared is proposed, and the configuration other than that for using the cam curve is strictly identical with the line configuration of the conventional art. Namely, the configuration of FIG. 22 is a line configuration in which a speed feedforward (V) and a torque compensator (A) by the CPU are added to a position control shown in FIG. 23 and using a conventional servo motor, and is within a range of a conventional control technique. When the speed command (V) and the acceleration command (A) are to be produced by the CPU based on the position pattern only, a differential process must be performed on the basis of the scan period. The speed command (V) and the acceleration command (A) which are produced in this way already lag behind the actual speed.
Therefore, the effect is reduced to one half its original one unless a countermeasure from the viewpoint of the predictive control is taken.
As described above, a system of the conventional art has a problem in that the traceability is so poor that the control accuracy is low.
It is an object of the invention to provide a method of controlling an electronic cam type rotary cutter, and a method of producing an electronic cam curve which, in a control of, for example, a rotary cutter or a continuous packaging machine which is driven by a servo motor, perform a correct position control while a position loop is formed in the whole region and an electronic cam control of a continuous correlation system extending to the next cycle is configured, enable a control due to the same algorithm that can automatically cope with both long and short cut lengths or bag lengths, remarkably improve the productivity in a short cutting operation, have an excellent traceability, and improve the control accuracy.
In order to attain the object, the invention is characterized in that, in a method of controlling an electronic cam type rotary cutter which is driven by a servo motor, and which is controlled in long and short cutting operations by different speed waveforms on the basis of an electronic cam curve, a position loop is formed in a whole region on the basis of an electronic cam curve, an electronic cam curve of a cubic function is used as a position pattern for a noncutting zone, and an electronic cam curve of a quadratic function is used as a speed pattern, whereby a control is enabled with causing a same algorithm to automatically cope with the long and short cutting operations and a change of a line speed.
According to this configuration, a correct position pattern which is to be controlled is previously prepared, and a position control is performed at every moment over the whole region including the cutting and noncutting zones on the basis of the position pattern, thereby enabling a correct cutting position control on the basis of an electronic cam curve. As the electronic cam curve, a cubic function is used for a position pattern, and a quadratic function is used for a speed pattern. By the control contents based on an algorithm in which continuous correlations between the position and the speed at the timing when the cutting operation is ended, and those at the timing when the cutting operation of the next cycle is started are maintained, a cutting position control can be configured which has an excellent traceability, and in which the same algorithm is enabled to automatically cope with the long and short cutting operations and a change of a line speed.
The invention is characterized in that, in a method of controlling an electronic cam type rotary cutter which is controlled in long and short cutting operations by different speed waveforms on the basis of an electronic cam curve, and in which a line speed is controlled to be reduced in the short cutting operation, a position loop is formed in a whole region on the basis of an electronic cam curve, an electronic cam curve of a cubic function is used as a position pattern for a noncutting zone, and an electronic cam curve of a quadratic function is used as a speed pattern, whereby necessity of reduction of the line speed is eliminated even in a length range which is shorter than a range of a conventional art, and a cutting operation is enabled while maintaining the line speed to 100%.
According to this configuration, the speed pattern based on the electronic cam curve is a quadratic curve, and a torque required for acceleration and deceleration in the noncutting zone is dispersed over the whole of the region, so that the root mean square of the torque is smaller than that in the case of a trapezoidal speed where the acceleration or deceleration time is somewhat short. In a short cutting operation where the acceleration or deceleration frequency is higher, particularly, the cutting is enabled even when the line speed is not lowered to a length which is shorter than that of a conventional art.
In the method of controlling an electronic cam type rotary cutter, preferably, a speed pattern of a spiral blade due to a cam curve diagram is, in a cutting zone, identical with the line speed, and, in the noncutting zone, a quadratic curve which is raised in the short cutting operation, and a quadratic curve which is reduced in the long cutting operation, and a speed pattern of a straight blade is a pattern which is different from the spiral blade in that only the speed in the cutting zone is proportional to 1/cosxcex8.
According to this configuration, both the spiral blade and the straight blade can be similarly controlled by a speed pattern of a quadratic curve. In the case of a straight blade, the speed pattern in the cutting zone is set to be 1/cosxcex8, thereby allowing a workpiece which continuously travels at the line speed, to be cut in a direction perpendicularly to the traveling direction in the same manner as the case of a spiral blade.
The invention is characterized in that, after a sealing work, a cutting work, or the like is performed in synchronization with a workpiece in a specific phase zone of one cycle of a rotary mechanism such as a lateral sealing mechanism of a vertical continuous packaging machine which is driven by a servo motor, or a rotary cutter which cuts a workpiece into a constant length, a cubic function is used in a position command according to a continuous correlation control system including a prediction to a start of a work in a next cycle, and a quadratic function is used in a speed feedforward, whereby an optimum electronic cam curve is obtained while allowing a bag length or a cut length of the workpiece to automatically perform correspondence irrespective of a value of peripheral length/M (M=1, 2, . . . , the number of sealing faces or blades).
According to this configuration, when a sealing or cutting work is to be performed in synchronization with the line speed of a film, paper, or another workpiece in a specific phase zone (a sealing zone or a cutting zone) in one cycle of the rotary mechanism, a position pattern is used as a position command, and a speed pattern is used as a speed feedforward by a continuous correlation control in which a cubic function is used as a cam curve (the position pattern) satisfying four boundary conditions of the final position and speed in the specific phase zone, and the initial position and speed in a specific phase zone of the next cycle, and a quadratic function that is its differential value is used as the speed pattern, and which includes a predictive control for the next cycle, and an electronic cam control in which the position and speed are again made coincident with the line speed at a initial time in the specific phase zone of the next cycle can be realized.
In the method of producing an electronic cam curve, preferably, a rotational speed n2 and a rotational position y2 of the lateral sealing mechanism or the cutting blade in the sealing zone or the cutting zone are
n2=N1xe2x80x83xe2x80x83(rpm)
y2=(1/Mxe2x88x92Y1)(Tcxe2x88x92t3)xc3x97(txe2x88x92Tc)+1/Mxe2x80x83xe2x80x83(rev)
where N1 is the line speed at a start point, Y1 is a rotational position of a cutting start point, t3 is a time of the cutting start point, and Tc is one cycle time,
a curve equation of the nonsealing zone or the noncutting zone is a cubic function having four coefficients satisfying four boundary conditions of velocities V1 and V2 and positions X1 and X2 at times T1 and T2, a position x and a speed v which is obtained by differentiating the position x are indicated by
x=At3+Bt2+Ct+Dxe2x80x83xe2x80x83(rev)
v=3At2+2Bt+Cxe2x80x83xe2x80x83(rps),
(T1, X1) and (T2, X2) are substituted into equation x, (T1, V1) and (T2, V2) are substituted into equation v, the equations are solved for A, B, C, and D, T1=0, T2=t3, X1=0, X2=Y1, V1=Nt/60, and V2=Nt/60 are obtain A, B, C, and D, and cam curve equations at a rotational speed=n1 and a rotational position=y1 in the nonsealing zone or the cutting zone, and the rotational speed n2 and the rotational position y2 in the sealing zone or the noncutting zone are obtained as
xe2x80x83n1=60(3At2+2Bt+C)speedxe2x80x83xe2x80x83(rpm)
n2=N1xe2x80x83xe2x80x83(rpm)
y1=At3+Bt2+Ct+D positionxe2x80x83xe2x80x83(rev)
y2=(1/Mxe2x88x92Y1)/(Tcxe2x88x92t3)xc3x97(txe2x88x92Tc)+1/Mxe2x80x83xe2x80x83(rev).
According to this configuration, when the coefficients of the four boundary conditions, (T1, X1) and (T2, X2), and (T1, V1) and (T2, V2) are substituted into the cubic function having four coefficients
position x=At3+Bt2+Ct+D, and
its differential equation or speed v=3At2+2Bt+C,
and the equations are solved for A, B, C, and D, the followings are obtained:
A={2(X1xe2x88x92X2)xe2x88x92(T1xe2x88x92T2)(V1+V2)}/K
B=[(V1xe2x88x92V2)(T1xe2x88x92T2)(T1 +2T2)xe2x88x923(T1+T2)xc3x97{X1xe2x88x92X2xe2x88x92V2(T1xe2x88x92T2)]}/K
C{6(X1xe2x88x92X2)T1xc2x7T2+3(T1+T2)(V1xc2x7T22xe2x88x922T12)+2(T12+T1T2+T22)(V2xc2x7T1xc2x7V1xe2x88x92T2)}/K
D=-[(Xxe2x88x92V1xc2x7T1)T22(3T1xe2x88x92T2)+(X2xe2x88x92V2xc2x7T2)T12(T1xe2x88x923T2)+2(V1xe2x88x92V2)T12xc2x7T22]/K
K=xe2x88x92(T1xe2x88x92T2)3.
When T1xe2x86x920 (the final time of the cutting or sealing zone), T2xe2x86x92t3 (the initial time of the cutting zone of the next cycle), X1xe2x86x920 (the position at time T1), X2xe2x86x92Y1 (the position at time T2=t3), V1xe2x86x92N1/60 (the speed at time T1=0), and V2xe2x86x92N1/60 (the speed at time t3) are substituted into thus obtained A, B, C, and D to obtain A, B, C, and D, it is possible to obtain a cam curve equations, n1=60(3At2+2Bt+C)
n2=N1
y1=At3+Bt2+Ct+D
xe2x80x83y2=(1/Mxe2x88x92Y1)/(Tcxe2x88x92t3)xc3x97(txe2x88x92Tc)+1/M.